Emerging Technology - UV Lasers

Building Faster Processors with Ultra Violet Laser Technology

Executive Summary

The proliferation of desktop computing, the Internet, client/server networking and advancements in software over the last ten years have had a tremendous effect on the way businesses operate. A key driver during this period has been the continued evolution of microprocessor engines that are common to every desktop machine. The expected increase in processor speed and power has become an enabling force for new business processes that promise to provide increased productivity and output of industry.

Some increases in processor power and speed have come about by reducing the size of semiconductor chips and the circuits within them. These steps serve to increase performance and lower cost by allowing more transistors on a chip and more chips on a wafer. UV laser (Ultra Violet) is an emerging technology that is utilized in the fabrication of microprocessors to ensure that this favorable trend continues into the future.

UV laser technology is the next step in providing faster micorprocessors at low cost enabling business to run powerful applications and increase communications.

Moore's Law

One of the critical concepts in microprocessor evolution is Moore's Law , named for Dr. Gordon Moore, chairman emeritus and founder of Intel. Moore's Law predicts a continuing increase in processing power and speed from generation to generation of new chips (essentially doubling the number of transistors on a microchip every 18 months). One of the methods processor manufacturers use to improve parameters in new chips is to literally reduce the size of the transistors that make up a microprocessor. The width of a semiconductor is referred to as the gate width and is typically about .4 microns wide (a micron in 1/25,000 of an inch). By reducing gate width, chip manufacturers can design chips with more transistors that are capable of operating at higher speeds. The higher speeds are a result of a decrease in the chips intrinsic "capacitance" which is directly related to the smaller gate width. Since this capacitance is reduced, the time it takes to "charge and discharge" the chip is reduced and hence the chip can run at higher "clock" speeds.

Manufacturing Chips

Semiconductor manufacturing begins with a thin, flat, round disc of pure silicon called a wafer. A wafer is usually 4 to 12 inches in diameter and is covered with a light-sensitive emulsion. Electronic circuits are "built" by projecting a circuit pattern onto small rectangular sites called a die with a light scanner. This process is called microlithography and is repeated across the entire surface of the wafer as many as 25 times (known as layering) per die. The individual die are then cut, bonded onto lead-wire and encapsulated in plastic or ceramic packages and sold as integrated circuits.

The lithographic illumination light source is a critical component of the manufacturing process. For the past 30 years, the light source has been the Mercury-arc lamp. These light sources have been able to keep up with Moore's Law by moving their light wavelenth from g-line (436 nanometers) to i-line (365 nanometers). However, the wide spectrum of light that is characteristic of Mercury-arc lamps degrades resolution and hence limits their effectiveness in achieving resolutions required for critical dimensions below .3 microns. If another light source were not available, circuits would stay about their current size which would jeopardize the entire semiconductor industry due to the repeal of Moore's Law. Thus, the continuation of Moore's Law into the future is threatened without the source of a new technology that can successfully etch semiconductor wafers below .3 microns.

UV Lasers to the Rescue

The latest-generation of lithography tools are UV-lasers based on the combination of krypton and fluorine atoms. These chemicals are combined to form a molecule known as an excited dimer, or "excimer". When pulsed with electrical energy this molecule will release invisible light with a wavelength of 248 nanometer that has just the right characteristic to image circuit patterns below the .3 micron dimension.

Next-generation argon fluoride based lasers promise even further reductions in semiconductor dimensions and are expected to be in production as early as the year 2000. Although not in operation today, these 193 nanometer lasers are receiving substantial support from leading semiconductor organizations such as Sematech, Austin, TX.

The graph below illustrates the capacity gains created by building chips with smaller and smaller geometries. For instance, by creating chips with .25 micron geometry, a X4 gain is realized in memory capacity when compared to .35 microns. (64 Mbytes to 256 Mbytes).

Graph of Capacity Gains

Source of Graph: cymer.com

Excimer Lasers

Improvements in reliability and reduced cost of operations have made the excimer laser ideal for mass-production environments. These lasers are manufactured by a hand-full of companies around the world including Cymer Inc., San Diego, CA, Lambda-physik R&D, a German-based subsidiary of Coherent, Inc. and Komatsu, Ltd., located in Japan. Cymer, who currently provides 80% of UV-lasers to the industry, has created a light source dubbed "Deep Ultra Violet" or DUV that promises gate widths as low as .25 microns with production equipment today with the promise to approach .1 microns in the future.

Chip Graphic

Source of Graphic: cymer.com

Since the most basic form of competition among semiconductor manufacturers is to be the first with the next-generation of faster chips, it is not surprising that almost all companies involved in lithography have pilot programs that involve UV lasers. According to Doug Marsh, president of US operation for ASM Lithography BV, "Last year, only 5% of our business was in UV lithography. This year it will be 30%, and we estimate 60% for next year". Indeed Cymer's backlog of order increased from $39.8 million to $98 million between the first and fourth quarters of 1996.

References

Authors

Special thanks to Drew Bairnsfather for help in web-page design.